1. Field of the Invention
The present invention relates to an electronic control device for use in a vehicle.
2. Description of Related Art
The number of electronic control devices mounted on a vehicle and power consumption of the vehicle are ever increasing with increasing complexity of the functions of the vehicle. Accordingly, it is strongly required to reduce power consumption of an electronic control device mounted on a vehicle, especially to reduce power consumption (dark current) of an electronic control device supplied with power all the time from a vehicle battery while the vehicle is parked. Although the dark current occurs by various causes, it is mainly due to circuit components including a microcomputer included in the electronic control device, which require power supply to operate even while the vehicle is not used.
Many methods have been proposed to reduce power consumption of a vehicle-mounted electronic control device supplied with power from a vehicle battery all the time, including the one in which a microcomputer is set in the so-called sleep mode to minimize the functions of the microcomputer while the vehicle is not used to reduce power consumption as much as possible while the vehicle is not used. Also, it is known to configure a microcomputer of a vehicle-mounted electronic control device to execute a predetermined operation at intermittent periods while the microcomputer is in the sleep mode in order to detect wake-up factors, so that the microcomputer recovers from the sleep mode quickly as necessary.
Further, it is proposed to set the intermittent periods differently for different time periods of a day to further reduce the dark current. For example, refer to Japanese patent Application Laid-open No. 2002-81239 (patent document 1). According to this proposal, a day is divided into a commuting time, a daytime and a late-night time, and the intermittent periods are set to increase in this order.
Further, there is known an electronic control device including a plurality of microcomputers and configured to detect wake-up factors by only a power supply IC thereof, in order to collectively control power supply and reset cancel of the microcomputers. For example, refer to Japanese Patent Application Laid-open No. 2007-30593 (patent document 2).
However, the technique disclosed in patent document 1 is not different from conventional techniques in that it requires performing an intermittent operation all the time, although the intermittent periods are set differently for different time periods of a day. Hence, the effect of reduction of the dark current is not large enough.
There is a concern in the technique disclosed in patent document 2 that power is consumed more than necessary because all the CPUs are woken up when a wake-up factor is detected regardless of whether all the CPUs are required to operate.
Further, since the power supply IC is configured to perform signal exchange with all the CPUs to determine whether a sleep condition is satisfied for the respective CPUs, and perform various processes including detection of wake-up factors to start power supply to the CPUs, the structure of the power supply IC itself becomes complicated causing power consumption thereof to increase. In addition, since the CPUs are not supplied with power at all and stop operation completely while they are in the sleep mode, the technique disclosed in patent document 2 cannot address the need for at least one of the CPUs to continue to execute essential minimal processes even during the sleep mode.